Deflection compensation for doctor backs



May 26, 1964 1. J. PHILLIPS DEFLECTION COMPENSATION FOR DOCTOR BCKS Filed octl 17. 1961 INVENTOIL frz/njrJPf/zja A ORNEYS United States Patent O 3,134,126 DEFLECTION COMPENSATION FOR DOCTOR BACKS Irving J. Phillips, South Beloit, 1li., assignor to Beloit Corporation, a corporation of Wisconsin Filed Oct. 17, 1961, Ser. No. 145,711 7 Claims. (Cl. 15-256.51)

This invention relates to improvements in doctor backs and more particularly relates to an improved apparatus and method, compensating for temperature differences on the doctor back and maintaining the doctor back and associated doctor blade true.

In the coating of paper webs, as the web picks up a layer of coating material a doctor blade maintains the layer of coating material picked up on the web uniform. ln order to assure a uniform coating across the width of the web, the pressure between the web and the doctor blade must be uniform throughout the entire width of the web, and the blade and blade holder must be straight and true and parallel to the face of the back-up roll about which the web travels.

Where the doctor back is subjected to a uniform ambient temperature, the blade holder may first be trued in the manner shown and described in an application Serial No. 139,939, filed September 22, 1961, by Arnold J. Schmidt and rving J. Phillips on and entitled System and Apparatus for Truing Doctor Blade Holders on Doctor Backs.

Where, however, there are temperature differences in the doctor back or in the area surrounding the doctor back, which may occur during the coating operation, due to heat from the coating material, or to dope added to the coating material or from the drier or calender rolls in the immediate vicinity of the doctor back, and also due to the friction of the blade on the web as it travels about the back-up roll, stresses will be introduced in the doctor back tending to distort or bow the doctor back and therefore affect the trueness of the doctor blade and the uniformity of the layer of coating to be applied to the web.

A principal object of the present invention is to overcome these diiculties by providing a simple method and apparatus for compensating for temperature differences on the doctor back during the operation of the doctor back.

A further object of the invention is to provide a simple and improved form of doctor, in which variations in temperature on the doctor back are compensated for by heating selected areas of the doctor back, to compensate for variations in temperature in the region of the doctor back.

Still another object of the invention is to improve upon the doctor backs heretofore in use, particularly in the .coating of paper webs traveling about back-up rolls, by

internally heating the doctor back for the length thereof and at selected areas within the doctor back, to compensate for variations in temperature on the doctor back.

A still further object of the invention is to provide an improved form of doctor back having means contained therein for iiowing heat energy along the doctor back in selected regions of the doctor back, to compensate for variations in temperature about the doctor back.

Still another object of the invention is to provide an improved form of hollow doctor back in which the interior of the doctor back is divided into compartments, and in which heat energy is admitted to selected compartment to flow therealong.

These and other objects of the invention will appear from time to time as the following specication proceeds and with reference to the accompanying drawings wherein:

FGURE l is a diagrammatic view, diagrammatically showing a doctor back and doctor blade in operative association with a web passing about a back-up roll of a coating applicator, and illustrating one form in which my invention may be embodied; and

FiGURE 2 is a diagrammatic view somewhat similar to FIGURE 1 and illustrating a modified form in which my invention may be embodied.

ln the embodiment of the invention illustrated in FIGURE l of the drawings, I have diagrammatically shown a web of paper 1t?, passing under a back-up roll 11 of a coating applicator. I have also shown a doctor blade 15 extending for the length of the back-up roll 11 in close proximity to said back-up roll and the web of paper, for maintaining the coating on the web uniform in thickness throughout the width of the web, in a conventional manner.

The doctor blade 15 is a part of a doctor assembly consisting generally in a doctor back 16 supported at its opposite ends on trunnions 17 for adjustable movement about an axis extending longitudinally of the doctor back. The doctor back 16 and blade 15 are held in position and adjustably moved about the trunnions 17 to bring the doctor blade 15 to the required spacing with respect to the web of paper 10, by suitable adjusting mechanism, which may be of any well known form and is no part of the present invention, so need not herein be shown or described further.

The doctor back 1d is shown as being in the form of a hollow beam, generally rectangular in cross-section, except for an outwardly flared front wall 19, terminating at a bottom face 2li of a blade holder 21 extending for the length of the doctor back. The blade holder 21 also has a rear face 22 abutting the forward end of a top wall 25 of the doctor back, and with the face 20 of the blade holder 21 closing the top advance side of the doctor back.

The doctor baclc 16 is shown in FEGURE 1 as having a vertical divider plate 24 extending along the hollow inner side thereof from one end thereof to the other and intermediate the ends of a bottom plate 2S of said doctor back. The partition 24 is abutted by partitions 25 and 26, extending horizontally from opposite vertical faces thereof, intermediate the ends thereof, and dividing the interior of the doctor back into four compartments 27a, 27]), 27C and 27d extending therealong for the length thereof. The partitions 24, 25 and 26 may be welded or otherwise secured to each other, and may also be Welded or otherwise secured to the hollow interior portion of the doctor back 15 to provide water tight compartments extending along said doctor back for the length thereof.

The blade holder 21 has a rear face 29 engaged by the blade 15 and terminating at its lower end portion in a recess 3@ and shoulder 31, forming a socket and support for a clamping bar 33. The clamping bar 33 has a forwardly facing shouldered recess 35 along which the blade 15 fits. The blade 15 has parallel spaced arcuate ribs extending along the forward face thereof, having interengagernent with the rear face 2% of the blade holder 21. The clamping bar 33 may clamp the blade 15 to the blade holder 21 in a conventional manner which is no part of the present invention so need not herein be shown or described.

Referring now in particular to the means for compensating for temperature differences to which the doctor back is subjected, and preventing bowing or deflection of the doctor back due to differences in temperature on the doctor back, the compartments 27a, 27b, 27C and 27d have pipes 37a, 37b, 37C and 37d respectively leading thereinto through an end wall 39 of the doctor back. The pipes 37a, 37b, 37C and 37a' are connected with a Valve 49, which may be connected with a source of heat such as steam or any other high temperature liquid or gas. The valve 4t? may be a four-way valve of a conventional form operable to supply heat energy to the four compartments 27a, 27h, 27e and 27d independently or simultaneously of each other.

Thus, when the compartment 27a closed by the blade holder 2l is subjected to high temperature conditions, and the other compartments 27h, 27C and 27d are subjected to lower temperature conditions, heat energy may be admitted into one or more of the compartments Z'7b, 27C or 27d, to effect the expansion of the doctor back subjected to normal temperatures at the rate of expansion of the portion doctor back subjected to external high temperature conditions.

The expansion of the section of the doctor back subjected to high temperature conditions may thus be compensated for and the temperature of the balance of the doctor back may be raised to the extent necessary t force the doctor back to return to its true condition.

The differences in temperature on the various faces of the doctor back may also be compensated for by admitting cold liquid or gas into the compartment 27a at a temperature sufficient to maintain the temperature of the doctor back uniform throughout its cross-section.

In FIGURE l, I have shown a one-way valve 4I connected to a source of cold for supplying cold liquid or gas to the pipe 37a leading into the compartment 27a to cool the temperature of the compartment 27a to the temperatures of the compartments 27b, 27C and 27d and to maintain the temperature across the doctor back uniform throughout the cross-section thereof.

t should also be understood that where the ambient temperature to which the doctor back is subjected is uniform and the doctor baclt may be distorted, due to dellecf, j

be individually heated by electrically energized means, f

such as resistor heaters, if desired.

In the form of the invention shown in FIGURE 2, the doctor back I6, blade holder 2l, blade I5 and clamping bar 33 are the same as in the form of the invention illustrated in FIGURE l. The same part numbers will be applied to the same parts in FIGURE 2 that were applied to FIGURE 1.

In the form of the invention illustrated in FIGURE 2, I have shown three pipes 43, t; and entering the doctor back adjacent one end thereof, and extending for the length thereof. Heated liquid or gas may be supplied to the pipes 43, 44 and 45 under the control of a valve 45, either individually or simultaneously, in accordance with the requirement for the heat required to bring the doctor back 16 and blade IS to its true form where it has become distorted by uneven temperatures thereon.

The three way valve 46 may be of a type that will admit hot liquid or gas to a selected pipe 43, 4d and 45 or to all three pipes at the same time.

It should here be understood that while I have described the distortion compensating means of the present invention as being manually controlled, that it may readily be automatically controlled by the signals created by a sheet caliper or thickness measuring device (not shown). The sheet caliper or thickness measuring device may signal the control valve controlling the admission of liquid or gas to the compartments or pipes extending along the hollow interior of the doctor back and effect the operation of said Valve as for example, to effect the flow of hot liquid or gas into the compartments 27h, 27C, and 27d in accordance with the requirements for compensating for distortion of the doctor back by elevated temperatures in compartment 27a and the region of said compartment. Cold air with liquid may also be admitted into the compartment 27a under the control of the sheet caliper or thickness measuring device in a suitable manner.

It may be seen from the foregoing that I have provided a simple method and apparatus for compensating for temperature differences within and along a doctor back, caused by heating of the doctor back by the coating material or dope added thereto, or the adjacent drier or calender roll or friction of the doctor blade on the web being coated, and thatthe doctor back and blade may be trued during operation of the doctor by simply equalizing the heat along and within the doctor back, to bring the doctor back up to and to maintain the doctor back at a uniform temperature throughout its cross-section for the length thereof.

It should further be understood that while I have shown and described the invention in connection with doctors used on coating machines, that the invention may also be applied to doctors used on presses, dryers and calender rolls or other similar applications.

While I have herein shown and described several forms in which my invention may be embodied, it should be understood that various other variations and modilications in the invention may be attained without departing from the spirit and scope of the novel concepts thereof, as defined by the claims appended hereto.

I claim as my invention:

1. A doctor back comprising:

(a) an elongated hollow body closed at its ends,

(b) a blade holdel extending `along said body and projecting therefrom,

y(c) a doctor lblade clamped to said blade holder and extending there-along and projecting therefrom,

(d) means providing for heat transfer along a plunality of areas, each extending 'along Kthe length of .said hollow body,

(e) and means selectively operable to vary the heat :transfer in selected of said areas.

2. A doctor comprising;

(a) an elongated hollow body closed at its ends,

(b) a blade holder extending along said body and projecting therefrom,

(c) a doctor blade clamped to said blade holder and extending therealong,

(d) internal partitions extending along the hollow interior of said body for substantially the -length thereof and dividing said body into a plurality of adjacent compartments one of which extends along said blade holder,

(e) and means for heating selected of said compartments remote from ysaid blade holder to compensate for temperature rises in the compartment extending along said blade holder.

3. :A doctor comprising;

(a) an elongated hollow body closed at its ends,

(b) `a blade holder extending along Said body and projecting therefrom,

(c) a doctor blade clamped yto said blade holder and extending therealong,

(d) internal partitions extending along `the hollow interior of said body for substantially the length thereof and dividing said body into a plurality of adjacent compartments,

(e) one of said compartments extending along said doctor blade holder and being in association therewith,

(f) and means for cooling said compartment extending along the blade holder to the temperature of the other of said compartments to maintain the temperature of said doctor back uniform throughout the cross-sectional area thereof.

4. A doctor comprising;

(a) an elongated hollow body' closed at its ends,

(b) a blade holder extending along said body and projecting therefrom,

(c) a doctor blade clamped to said blade holder and extending therealong,

(d) interna-1 partitions extending along the hollow interior of said body for substantially the length thereof and dividing said body into a plurality of adjacent compartments one of which extends along said blade holder,

(e) and means for flowing heated uid through selected of said `compartments remote from said blade holder to maintain the temperature of said doctor back uniform throughout the cross-sectional area thereof.

5. A doctor comprising;

(a) an elongated hollow body closed at its ends,

(b) a blade holder extending along said body and projecting therefrom,

(c) a doctor blade clamped to said blade holder and extending therealong,

(d) internal partitions extending along the hollow interior of said tbody for substantially the length thereof and dividing said body into at least four adjacent compartments,

(e) means for heating at least three of said comparttments and for cooling 'the fourth of said compartments, to maintain the temperature of said doctor back uniform throughout the cross-sectional area thereof.

6. A doctor comprising;

(a) an elongated hollow body closed at its ends,

(b) a blade holder extending along said body and projecting therefrom,

(c) a doctor blade clamped to said blade holder and extending therealong,

(d) a plurality of pipes extending along the hollow interior portion of said body along regions remote from said blade holder,

(e) and means for supplying heated fluid to selected of said pipes and owing heated iluid therethrough.

7. A doctor comprising;

(a) an elongated hollow body closed at its ends,

(b) a blade holder extending along said body and projecting therefrom,

(c) a doctor blade clamped to said blade holder and extending therealong,

(d) a plurality of pipes extending 'along the hollow interior portion of said body along regions remote from said blade holder,

(e) a control valve having connection with a source of heat and having connection lwith said pipes and operable Ito eifect the ow of heated fluid through selected of said pipes, 'to maintain the temperature of said doctor back uniform throughout the crossseotional area thereof.

References Cited in the tile of this patent UNITED STATES PATENTS 1,922,220 Sprague Aug. 15, 1933 2,209,257 Blank July 23, 1940 3,001,296 Carvill Sept. 26, 1961 

1. A DOCTOR BACK COMPRISING: (A) AN ELONGATED HOLLOW BODY CLOSED AT ITS ENDS, (B) A BLADE HOLDER EXTENDING ALONG SAID BODY AND PROJECTING THEREFROM, (C) A DOCTOR BLADE CLAMPED TO SAID BLADE HOLDER AND EXTENDING THEREALONG AND PROJECTING THEREFROM, (D) MEANS PROVIDING FOR HEAT TRANSFER ALONG A PLURALITY OF AREAS, EACH EXTENDING ALONG THE LENGTH OF SAID HOLLOW BODY, (E) AND MEANS SELECTIVELY OPERABLE TO VARY THE HEAT TRANSFER IN SELECTED OF SAID AREAS. 